chore: update Dependabot schedule to quarterly (3 months)

[graycreate]

Summary

• Updated Dependabot schedule from monthly to quarterly for both Gradle dependencies and GitHub Actions
• This reduces the frequency of dependency update PRs from every month to every 3 months

Changes

• .github/dependabot.yml: Changed interval from monthly to quarterly for both package ecosystems

Rationale

• Reduces PR noise while still keeping dependencies reasonably up-to-date
• Quarterly updates align with typical release cycles for most dependencies
• Allows more time to batch and test dependency updates together

[Copilot]

Pull Request Overview

Updates Dependabot configuration to reduce the frequency of dependency update PRs from monthly to quarterly intervals, balancing maintenance overhead with keeping dependencies reasonably current.

• Changed update schedule from monthly to quarterly for both Gradle dependencies and GitHub Actions
• Maintains existing time settings and pull request limits while reducing update frequency